The present invention relates to a color-filter manufacturing method of manufacturing a color filter by discharging ink to a color-subject material with the use of an ink-jet head, a color filter, display apparatus and an apparatus including the display apparatus.
Generally, a liquid crystal display apparatus is used in a personal computer, word processor, pachinko (Japanese pinball game) table, automobile navigation system, small-sized television set and the like, and its demands are increasing recently. However, since the price of a liquid crystal display apparatus is high, the need for cost reduction is increasing every year for a liquid crystal display apparatus.
A color filter which constitutes a liquid crystal display apparatus includes columns of pixels in red (R), green (G) and blue (B), arrayed on a transparent substrate. In the periphery of each of these pixels, a black matrix for shielding light is provided in order to enhance displaying contrast.
The conventionally known methods of manufacturing a color filter are: pigment dispersion method, dyeing method, electrodeposition method and print method.
In the pigment dispersion method, a pigment-dispersed photosensitive resin layer is formed on a substrate and patterned into a single-color pattern. This process is repeated three times to obtain R, G, and B color filter layers.
In the dyeing method, a water-soluble polymer material as a dyeable material is applied onto a glass substrate, and the coating is patterned into a desired shape by a photolithographic process. The obtained pattern is dipped in a dye bath to obtain a colored pattern. This process is repeated three times to form R, G, and B color filter layers.
In the electrodeposition method, a transparent electrode is patterned on a substrate, and the resultant structure is dipped in an electrodeposition coating fluid containing a pigment, a resin, an electrolyte, and the like to be colored in the first color by electrodeposition. This process is repeated three times to form R, G, and B color filter layers. Finally, these layers are calcined.
In the print method, a pigment is dispersed in a thermosetting resin, a print operation is performed three times to form R, G, and B coatings separately, and the resins are thermoset, thereby forming colored layers. In all of the above methods, a protective layer is generally formed on the colored layers.
The point common to these four methods is that the same process must be repeated three times to obtain layers colored in three colors, i.e., R, G, and B. Because of the large number of processing steps, these methods have disadvantages such as decreased yield and increased cost.
Furthermore, in the electrodeposition method, limitations are imposed on pattern shapes which can be formed. For this reason, with the existing techniques, it is difficult to apply this method to TFTs. Moreover, in the print method, a pattern with a fine pitch is difficult to form because of poor resolution.
In order to eliminate these drawbacks, there is a proposed technique in which a pattern of a color filter is formed by discharging ink onto a glass substrate by using an ink-jet head.
Regarding such ink-jet method, for instance, Japanese Patent Application Laid-Open No. 59-75205 discloses a technique where ink having three colors of pigment (R, G and B) is discharged on a substrate by ink-jet method and each ink is dried to form a colored image portion. Such ink-jet method enables to form pixels colored in R, G and B all at once. Therefore, the manufacturing process can be greatly simplified and large cost-down effect can be attained.
However, when a color filter is manufactured by the ink-jet method, a problem arises in that, in a case where each of the pixels in one column or one row of screen surface is serially colored by single scanning operation as shown in FIG. 11, color unevenness is generated in the screen.
It is considered that such color unevenness generated in the screen is caused by the following various factors related to non-uniform ink discharge.
(1) Fluctuation in the amount of ink discharged per single discharge operation; PA0 (2) Fluctuation in the diameter of ink discharged and spread on the substrate; and PA0 (3) Fluctuation in the positional relation of ink, spread on the substrate, with respect to the pixel.
Among the above three factors, factor (1) is recognized as color unevenness because color density of each pixel is different. Factors (2) and (3) are recognized as color unevenness because when macroscopically viewed, the color density of each pixel is viewed differently due to the non-uniform coloring of each pixel.
The reason that such fluctuation is viewed as color unevenness is described below with reference to FIG. 17.
FIG. 17 shows pixels of a color filter and absorbance distribution on the cross section of the pixels (to simplify the description, a single-colored color filter is shown).
In FIG. 17, pixel 1 has absorbance distribution of a pixel equivalent to that of pixels 2, 4 and 5. However, absorbance of pixel 1 is lower than that of pixels 2, 4 and 5. This is caused by the aforementioned factor (1). Meanwhile in pixel 3, the discharged positions are offset to the left. Therefore, although pixel 3 has the average absorbance equal to that of pixels 2, 4 and 5, distribution is different. This is caused by the aforementioned factors (2) and (3). In this example, since the right side of pixel 3 appears light, human eyes recognize pixel 3 lighter than pixels 2, 4 and 5. Therefore, this may be viewed as color unevenness.
Such non-uniformity of ink discharge exists not only in a single nozzle but also exists amongst plural nozzles.
Therefore, when a plurality of nozzles are used to speed up the coloring process, the above problem becomes particularly significant.
To cope with this problem, Japanese Patent Application Laid-Open No. 8-240803 proposes a method of dispersing the non-uniformity by setting limitation to the coloring order of pixels.
However, since such method constrains the coloring order of pixels, a problem arises in that it is difficult to reduce time required for coloring processes.